Booboo/Cudmore/Ashmore stayed longer because they didn't have other commitments. They were in Montreal for a while, but they weren't on set every day. That's why we'd always get tweets from them about going to dinner, or hanging out with someone, or sight seeing. Since they were all free of other commitments, their scenes weren't so much of a priority.

Berry and Paquin, on the there hand, forced the production to schedule all their scenes in a matter of days/weeks. So they were on set all day, for an extended period of time.